Ready Steady Eddy

[cncJim]

Also, and this is very important but open to interpretation, I am not removing power from the spindle inverter during emergency stop, I mentioned this is another post. The reason is that the inverter can stop the spindle faster than it will stop on it's own, it does this by applying dynamic braking. Other options for bringing the spindle to a timely halt would be a spring loaded mechanical brake or as in the case of my table saw, a DC injection braking system. Removing power to the inverter via a contactor is the obvious emergency stop strategy and it could be said that removing power from the inverter under load will damage it, that might be true but better to have a damaged inverter than a damaged limb. According to the machinery Regs. which won't apply in a private houshold situation, the spindle should stop within 10 seconds, now I've not had my spindle up to speed yet so time will tell how long it takes to stop on it's own.

Good info, thanks.
If I had your VFD rather than my cheap Chinese one, I might be more inclined to trust it to stop the spindle during an Estop as well.

Removing power to the inverter via a contactor is the obvious emergency stop strategy and it could be said that removing power from the inverter under load will damage it, that might be true but better to have a damaged inverter than a damaged limb.

Why would the inverter be damaged in this situation? Is it because once the power is cut to the inverter the spindle acts as a generator and this generated current can damage the inverter?

I would like to have a safety system that does not compromise at all on safety but has the best chance on leaving the equipment undamaged (also how do you test an estop circuit if testing it may damage the equipment?!?).

I'm not that keen on the mechanical breaking solution, so that leaves the following:-

EStop

• Dynamic/Rheostatic braking
  Cut cables from inverter to spindle and attach spindle to a bank of breaking resisters to apply dynamic breaking (is this even how it works!?!). At same time cut the run cable to the inverter.
• DC injection braking system
  Same as above but DC injection brake cuts the link from inverter to spindle and applies DC to the spindle to stop it.

I like the idea of the DC injection braking system but they seem pretty expensive (RS DC Injection Brake @ ~£160 with VAT!). I wonder how easy/cheap it would be to do dynamic braking (without the vfd)?

edit - Just noticed my Huanyang vfd has terminals to add a braking resistor. If power is removed from the inverter would this still be used/effective? would it cause damage to the inverter?

[Jonathan]

Removing power to the inverter via a contactor is the obvious emergency stop strategy and it could be said that removing power from the inverter under load will damage it, that might be true but better to have a damaged inverter than a damaged limb.

Unlikely to cause significant damage to your limbs due to spindle's low inertia, so personally I'd rather it damaged the limb as that'll get fixed for free on the NHS, unlike the VFD.

Why would the inverter be damaged in this situation? Is it because once the power is cut to the inverter the spindle acts as a generator and this generated current can damage the inverter?

Vaguely.

Just noticed my Huanyang vfd has terminals to add a braking resistor. If power is removed from the inverter would this still be used/effective? would it cause damage to the inverter?

If you remove the power, the inverter can't do anything as it will only remain switched on for less than 1/10th of a second before the capacitors discharge. So no, it wont apply the brake.

I would like to have a safety system that does not compromise at all on safety but has the best chance on leaving the equipment undamaged

In that case you need to separate 'fault conditions' from safety concerns - e.g hitting a limit switch or stepper driver fault signals do not pose safety hazards, so treat them as such and wire it so the machine just pauses. The only one that warrants fast and complete shutdown is pressing the e-stop, as that's what you can supposedly do if you're about to get hurt.

Now regards the Kill power or Kill signal to VFD then I used to be Kill Signal guy but I'm now I Kill all power. Reason being what happens if the signal breaks or Even the VFD goes faulty.?

The signal should be wired such that if the wire's broken or otherwise interfered with the signal changes state and the system stops. The VFD going faulty sounds exceptionally unlikely, but if you're worried about that then just have a timed relay to switch the VFD power off a couple of seconds after the signal (as mentioned earlier), since by that point the spindle will have stopped so you wont damage the VFD by cutting the power, and if it's not stopped then the VFD has gone faulty so you probably don't care about risking damage to it by cutting the power.

E-stop is hit due to Limit or some other none spindle related condition then doesn't really matter how long spindle takes to slow down and coasting to a stop isn't long or problem.

My new spindle takes 107 seconds to stop from full speed if left to coast. I tend to agree that it's not really a problem though.

*emergency stop button pressed - strategy 1 or 2

Two, see above. You could take advantage of the enable signal on the stepper drivers to disable them, then link cutting the power to the delay associated with the VFD.

I also think the braking resistor is not required because of the fairly low inertia of the load.

Yes - the internal resistor is sufficient to stop the 2.2kW spindles in less than a second, so you can easily implement the above method.

(3000th post... )

[JAZZCNC]

The VFD going faulty sounds exceptionally unlikely

Not that unlikely really has I've got one here that did just that in that it wouldn't turn off thru a signal or the control panel. Turned out to be faulty panel and was replaced by ABB but the fact was it stayed bloody on so no signal would have turned it off.!!

[Jonathan]

Not that unlikely really has I've got one here that did just that in that it wouldn't turn off thru a signal or the control panel. Turned out to be faulty panel and was replaced by ABB but the fact was it stayed bloody on so no signal would have turned it off.!!

What's your point? The timed switch off mentioned twice (now three times) in this thread would have turned it off. Also you can't judge how likely something is with such a small sample size.

A couple of months ago I got a 15kW ABB VFD. Wired it up correctly and 5 minutes later the input rectifier blew up leaving my ears ringing for about half an hour!

[JAZZCNC]

What's your point? The timed switch off mentioned twice (now three times) in this thread would have turned it off. Also you can't judge how likely something is with such a small sample size.

Point is that it does happen and equally you can't say it's unlikely because it has happened.!! . . . . . Agree thou it's irrelevant has it will be safe eventually if power cutoff is just delayed. ( I was more meaning it's unsafe if just relying on Signals.)